Issue 13, October 8, 2021

Common Weed Control Mistakes

As Groucho Marx put it so well, “Learn from the mistakes of others.  You can never live long enough to make them all yourself.”  I’m hopeful my kids will take this lesson to heart.  Fortunately, we learn from our mistakes, most of the time.  Preventing mistakes is best, but we are all humans and mistakes are unavoidable.  Maybe you have seen the bumper sticker, “Mistaeks Happen”.   

Often mistakes happen in weed control.  Many are preventable simply by carefully reading, understanding, and following the herbicide label.  Spills can be prevented but let’s face it, they still happen. 

In addition to the label directions being understood, the herbicide mode of action should also be understood at least somewhat.  How is it taken up by the plant?  Where does it need to be put so uptake can occur?  A gentleman told me once that he had tried to use a herbicide on his tree seedlings growing around his house and his control attempts were unsuccessful.  We discussed his application methods and he said that he knew trees took things up from the roots.  Therefore, he applied the herbicide to the ground.  Unfortunately, his herbicide should have been applied to the leaves.  Had he read the label?  No.

Does the herbicide move in the plant?  Is it systemic?  If so, patience is needed as it will take a while for injury symptoms to appear on the leaves followed by complete kill if all goes well.  Once I was hired to do some garden work for a professor.  She had me spray some weeds with a systemic herbicide.  Upon completion of that activity, I inquired about my next task.  She gave it some thought, handed me a knife, and told me to return to the weeds I had just sprayed and cut them down.  We then had a little chat about how her herbicide works and that patience and time were needed.  

How much herbicide is needed to kill unwanted weeds?  If a little is good, isn’t more better?  No.  That line of reasoning only works with things like chocolate.  Some would argue it won’t even work with that.  Again, the product label will give specific guidance on rates.  The maximum rate should never be exceeded.  Rates have been carefully evaluated to determine what is most effective.  Herbicide rates that are too high can result in poor weed control due to damaged or burned plant tissue which prevents absorption into the plant.  It’s like setting out to break into a house by picking the lock on the door, but first you set fire to the door.  Entering is going to be challenging. 

Certainly too much of a herbicide can reduce control but so can too little and placement is also important.  Obtaining uniform coverage of applications can be tricky and skips in the pass can lead to unaffected weeds.  Perhaps a uniform preemergent application is made but a well-meaning gardener or dog digs up the area and destroys that chemical barrier that was intended to prevent weed growth.  Or maybe a herbicide wasn’t used at all but mulch was applied to cover the soil and prevent germination.  If new plants are added to the site and care isn’t taken to keep dug up soil from mixing in with the mulch, you can guess what will happen.  Odds are good that there are weed seeds in the newly displaced soil. 

The soil being mixed with this mulch likely contains weed seeds. Michelle Wiesbrook. University of Illinois.

That takes us to tillage, which works well to remove smaller weeds.  Unfortunately, bare soil won’t stay bare and new weeds will return.  Tillage isn’t necessarily a mistake but thinking you’ll need to till only once is.  Tillage moves buried weed seeds up to the surface where they can then receive enough sunlight to germinate.  So plan to repeat tillage or better yet, invest in a winged weeder that cuts weeds just below the surface without disturbing the soil surface. In my experience, these don’t work perfectly but they do minimize soil disturbance compared to a traditional hoe.

What about homemade herbicide mixtures?  Aren’t they safer and less expensive than traditionally manufactured herbicides?  Recipes abound on the internet but they aren’t recommended.  It’s best to use research based products that come with labels that provide application specifics and tell you how to properly cover up your body just in case something goes wrong and the weed killer ends up in your eye (vinegar is caustic by the way).  A weed scientist in Wyoming once compared a “homemade” herbicide recipe to glyphosate.  He took a close look at the effectiveness, cost, and toxicity of both and added a dose of humor.  Learn what he discovered here:  There are vinegar-containing EPA registered products available in a garden center near you.  Check them out!  But it helps to know what type of weed you are trying to control, yet, another mistake commonly made!  Vinegar burns off the top growth and won’t move down into the roots.  Just like the Terminator, your perennial weeds will be back!  

One last mistake is allowing weeds to develop seeds or letting those seedheads remain on site.  It’s late in the growing season.  Our landscapes likely have more weeds than we care to admit.  Usually the heat makes us retreat to the cooler house.  We’re tired and weary and perhaps ready for frost so the last zucchini plant will finally die.  We’ll start fresh next year.  But allowing weed seeds to stay ensures more work for the next several years.  The old saying, “One year’s seeding makes seven years’ weeding” is sadly inaccurate when it comes to certain weeds that may remain viable for say 50 years.  If hand removal of the entire weed seems too daunting, simply pull out or cut off the tops and bag them for disposal. 

Finally, don’t spend too much time worrying about your mistakes.  Mistakes become experience.

Michelle Wiesbrook

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